This invention relates to the treatment of gastroduodenal disease associated with Helicobacter pylori infection and in particular it relates to the use of active immunisation as a treatment for H. pylorixe2x80x94associated gastroduodenal disease.
The bacterium, Helicobacter pylori, is now well established as a major gastroduodenal pathogen, and more than 50% of the world population is infected with this organism which causes gastritis of varying severity. While no symptoms are apparent in a great proportion of infected persons, in a significant number of H. pylori infected persons overt disease may result. The majority (95%) of duodenal ulcers are associated with H. pylori infection; a causal role is shown by treatment studies which indicate that if the organisms can be eradicated at the time of ulcer healing then the ulcers do not recurxe2x80x94in contrast to 80% recurrence rate at one year in those who remain infected with the organisms. Furthermore, up to 80% of gastric ulcers are thought to be H. pylori associated (Blaser, 1992).
There is now increasing evidence of the harmful consequence of long term H. pylori infection. In countries such as China, Colombia and Japan the bacterium is picked up very early in life, and in these persons the gastritis slowly progresses until after 30-40 years of continual infection, severe gastric atrophy appears. Gastric atrophy is well documented as being the precursor lesion for gastric cancer, although the actual cancer that develops in an atrophied stomach is dependent on a myriad of other factors including diet. However, all the evidence to date would suggest that the cancer would not develop if it was possible to remove the H. pylori infection at an early age before the atrophy had developed (Parsonnet et al., 1991).
There is no laboratory animal model of H. pylori infection that can be used for large scale assessment of new anti-H. pylori therapies. However, a Helicobacter felis mouse model of gastric Helicobacter infection has been developed that has proved extremely useful in the screening of the potential of new antimicrobial therapeutic regimens. H. felis is a spiral shaped bacterium that is very closely related to H. pylori. This bacterium colonises the stomach of mice in a very similar way to H. pylori in the human, i.e. the main ecological niche is gastric mucus and the localisation of colonisation is antral dominant. In germfree mice, H. felis infection induces a gastritis that is very similar to the human H. pylori infection with a chronic inflammation accompanied by polymorphonuclear leucocyte infiltration. Infection with each organism results in the induction of a similar raised immune response against H. pylori and H. felis respectively (Lee et al., 1990).
The H. felis mouse model has proved to be very predictive of the efficacy of anti-H. pylori agents in humans. Thus, monotherapy with agents with high in vitro activity such as erythromycin show no significant in vivo effect against H. felis in mice, just as erythromycin has no anti-H. pylori effect in humans despite high antimicrobial effects in vitro. In contrast, the triple therapy regimens of a bismuth compound, metronidazole, and tetracycline or amoxycillin lead to a very high eradication rate in H. felis infected mice (Dick-Hegedus and Lee, 1991). Such triple therapies are the most successful human anti-H. pylori regimens, and at the present time are recommended as the first choice for anti-H. pylori therapy. However, established Helicobacter infections are difficult to treat, and current chemotherapeutic regimens remain suboptimal due to problems with efficacy, toxicity, drug resistance and reinfection (O""Connor, 1992).
Active immunisation of already infected patients has not been proven efficacious for any clinically manifest human infectious disease (Burke, 1992). Given that H. pylori infections persist for long periods, if not the life of the infected individual, despite the presence of a vigorous immune response that includes a high level of circulating IgG antibody in the serum and the demonstration of local specific IgA antibody in the gastric mucosa, it has been considered that active immunisation was unlikely to be effective in therapy (Goodwin, 1993). Indeed, Czinn et al. (1993) in proposing that oral vaccination may be a feasible approach for the prevention of H. pylori infection in humans (based on an evaluation of an oral immunisation protocol in the H. felis mouse model), suggested that once infection is established neither antibody nor antibiotics are very effective at eradication.
Varga et al. (1992) have reported that a H. pylori vaccine prepared from organisms derived from a patient, and injected parenterally into that patient, resulted in an allergic reaction and failure to eradicate the organism.
Surprisingly, it has now been discovered for the first time that there is indeed a therapeutic potential for active immunisation against gastric Helicobacter infection. Furthermore, it has been discovered that oral administration of H. pylori antigen, with a suitable mucosal adjuvant, does not result in allergic or hypersensitivity symptoms, but results in suppression or eradication of the infecting organisms from the gastric mucosa.
According to one aspect of the present invention, there is provided a method for the treatment of Helicobacter infection in a mammalian host, which comprises the oral administration to said infected host of an immunologically effective amount of one or more Helicobacter antigen(s), optionally in association with a mucosal adjuvant.
In another aspect, there is provided a vaccine composition for the treatment of Helicobacter infection in a mammalian host, which comprises an immunologically effective amount of one or more Helicobacter antigen(s), optionally in association with a mucosal adjuvant.
In yet another aspect, the present invention provides the use of a vaccine composition comprising an immunologically effective amount of one or more Helicobacter antigen(s), optionally in association with a mucosal adjuvant. in the treatment of Helicobacter infection in a mammalian host.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
By use of the term xe2x80x9cimmunologically effective amountxe2x80x9d herein, it is meant that the administration of that amount to an individual infected host, either in a single dose or as part of a series, is effective for treatment of Helicobacter infection. This amount varies depending upon the health and physical condition of the individual to be treated, the taxonomic group of individual to be treated, the capacity of the individual""s immune system to synthesise antibodies, the degree of protection desired, the formulation of the vaccine, the assessment of the medical situation, and other relevant factors. It is expected that the amount will all in a relatively broad range that can be determined through routine trials.
The Helicobacter antigen(s) used in accordance with the present invention may be H. felis antigen(s), or more preferably H. pylori antigen(s). In a particularly preferred aspect of the present invention, a vaccine composition comprising H. pylori antigen(s) in association with a mucosal adjuvant is used the treatment of H. pylori infection in a human patient.
Preferably, the Helicobacter antigen(s) comprise a bacterial sonicate, and in particular a H. pylori sonicate. More preferably, the Helicobacter antigen(s) used in accordance with the present invention comprise inactivated whole bacterial cells of H. pylori. 
Alternatively, the Helicobacter antigen(s) used in accordance with the present invention may comprise one or more individual antigens, particularly one or more H. pylori antigens such as H. pylori urease, or H. pylori cytotoxin (CT), Cytotoxin Associated Immunodominant (CAI) antigen or heat shock protein (hsp) as disclosed by way of example in International Patent Publication No. WO 93/18150.
One mucosal adjuvant which is optionally, and preferably, administered with the Helicobacter antigen(s) to the infected host is cholera toxin. Another preferred mucosal adjuvant which may be administered with the Helicobacter antigen(s) is E. coli heat labile toxin (E. coli HLT). Mucosal adjuvants other than cholera toxin and E. coli HLT which may be used in accordance with the present invention include non-toxic derivatives of cholera toxin, such as the B sub-unit (CTB), chemically modified cholera toxin, or related proteins produced by modification of the cholera toxin amino acid sequence. Each of these molecules with mucosal adjuvant or delivery properties may be added to, or conjugated with, the Helicobacter antigen(s). Other compounds with mucosal adjuvant or delivery activity may be used, such as: bile; polycations such as DEAE-dextran and polyornithine; detergents such as sodium dodecyl benzene sulphate; lipid-conjugated materials; antibiotics such as streptomycin; vitamin A; and other compounds that alter the structural or functional integrity of mucosal surfaces. Other mucosally active compounds include derivatives of microbial structures such as MDP; acridine and cimetidine.
Helicobacter antigen(s) may be delivered in accordance with this invention in ISCOMS (immune stimulating complexes), ISCOMS containing CTB, liposomes or encapsulated in compounds such as acrylates or poly(DL-lactide-co-glycoside) to form microspheres of a size suited to adsorption by M cells. Alternatively, micro or nanoparticles may be covalently attached to molecules such as vitamin B12 which have specific gut receptors. Antigen(s) may also be incorporated into oily emulsions and delivered orally. Ail extensive though not exhaustive list of adjuvants can be found in Cox and Coulter, 1992.
Other adjuvants, as well as conventional pharmaceutically acceptable carriers, excipients, buffers or diluents, may also be included in the therapeutic vaccine composition of this invention. The vaccine composition may, for example, be formulated in enteric coated gelatine capsules including sodium bicarbonate buffers together with the Helicobacter antigen(s) and mucosal adjuvant.
Generally, a vaccine composition in accordance with the present invention will comprise an immunologically effective amount of Helicobacter antigen(s), and optionally a mucosal adjuvant, in conjunction with one or more conventional pharmaceutically acceptable carriers and/or diluents. As used herein xe2x80x9cpharmaceutically acceptable carriers and/or diluentsxe2x80x9d include any and all solvents, dispersion media, aqueous solutions, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents and the like. The use of such media and agents for pharmaceutical active substances is well known in the art and is described by way of example in Remington""s Pharmaceutical Sciences, 18th Edition, 1990, Mack Publishing Company, Pennsylvania, U.S.A..
The pharmaceutical composition of this invention may be orally administered directly to the mammalian host, for example, with an inert diluent or with an assimilable edible carrier, or it may be enclosed in hard or soft shell gelatine capsule, or it may be compressed into tablets, or it may be incorporated directly with the solid or liquid food of the diet. For oral therapeutic administration, the active compound may be incorporated with excipients and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. The percentage of active component in the compositions and preparations may of course be varied and is such that a suitable dosage will be obtained to be immunologically effective.
Solid oral dosage units such as tablets. troches, pills, capsules and the like may also contain the following: a binder such as gum tragacanth, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, lactose or saccharin may be added or a flavouring agent such as peppermint, oil of wintergreen, or cherry flavouring. When the dosage unit form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier. Various other materials may be present as coatings or to otherwise modify the physical form of the dosage unit. For instance, tablets, pills or capsules may be coated with shellac, sugar or both. A syrup or elixir may contain the active component, sucrose as a sweetening agent, methyl and prophylparabens as preservatives, a dye and flavouring such as cherry or orange flavour. Of course, any material used in preparing any dosage unit form should be pharmaceutically pure and substantially non-toxic in the amounts employed.
The vaccine composition of the invention is administered orally in amounts readily determined by persons of ordinary skill in this art. Thus, for adults a suitable dosage would be in the range of 10 xcexcg to 10 g, for example 50 xcexcg to 3 g. Similar dosage ranges would be applicable for children.
As noted above, a suitable mucosal adjuvant is cholera toxin. The amount of mucosal adjuvant employed depends on the type of mucosal adjuvant used. For example, when the mucosal adjuvant is cholera toxin, it is suitably used in an amount of 10 nanogram to 50 xcexcg, for example 01 xcexcg to 10 xcexcg. When the mucosal adjuvant is E. coli heat labile toxin, suitable amounts are 1 xcexcg to 1 mg, for example 5 xcexcg to 50 xcexcg.
In work leading to the present invention, active immunisation of mice previously infected with H. felis , with oral doses of cholera toxin or E. coli HLT adjuvant and a whole cell H. felis or H. pylori sonicate, result in the clearance of H. felis from the gastric mucosa. It is therefore anticipated that active immunisation of infected humans with oral doses of a mucosal adjuvant with H. pylori antigen(s) will result in the clearance of H. pylori from the gastric mucosa. Based on previous studies with this model using anti-H. pylori agents, it is considered that this is the first evidence of the therapeutic potential of active immunisation with H. pylori vaccines, and indicates that a vaccine composition for the therapy of human H. pylorixe2x80x94associated gastroduodenal disease is a preparation of Helicobacter antigen(s), optionally and preferably combined with a mucosal adjuvant.
It will be apparent to persons skilled in the field that effective treatment of Helicobacter pylori infection in humans with an oral vaccine composition of Helicobacter antigen(s) which will eradicate or suppress the infection will provide a significant therapeutic benefit via the suppression or elimination of gastritis, prevention of peptic ulcer relapse and reduction in the harmful sequelae of Helicobacter pylori infection including peptic ulceration and gastric cancer.